Re: Matt. 12:31. I have always understood the unforgivable sin as blasphemy against the Holy Spirit, because when Christ was on earth, the religious leaders were attributing his miracles to demonic powers when they were the product of the Holy Spirit.
The Pharisees were life long students of the Scriptures and knew better than to say the Lord’s miracles were coming from Satan, because their Scriptures foretold that the Messiah would perform the miracles Jesus performed. Therefore they were deliberately bearing false witness, a violation of the 9th commandment.
But they didn’t have the Holy Spirit sealed within them as we do. Because of our relationship with the Holy Spirit it’s not possible for a believer today to say such a thing (1 Cor. 12:3), and every sin an unbeliever commits will be forgiven when he or she comes to the Lord (Colossians 2:13-14).